The present invention relates to a durable outsole for an article of footwear. More particularly, the invention relates to a thermoplastic polyurethane outsole for an article of footwear having dispersed fluorocarbon additives, preferably perfluoropolyether (xe2x80x9cPFPExe2x80x9d) additive, in the ground engaging portions of the outsole, such as a cleat of a cleated athletic shoe, thereby improving wear resistance and traction of the outsole.
Modern articles of footwear, such as athletic shoes, are a highly refined combination of many elements which have specific functions, all of which work together for the support and protection of the foot. Athletic shoes today are as varied in design and purpose as are the rules for the sports in which the shoes are worn. Tennis shoes, racquetball shoes, basketball shoes, running shoes, soccer shoes, baseball shoes, football shoes, walking shoes, etc. are all designed to be used in very specific, and very different, ways. They are also designed to provide a unique and specific combination of traction, support and protection to enhance performance.
In general, an athletic shoe is divided into two general parts, an upper and a sole. The upper is designed to snugly and comfortably enclose the foot. Typically, it will have several layers including a weather and wear-resistant outer layer of leather or synthetic material, such as nylon, and a soft, padded inner layer for foot comfort.
The sole provides a broad, stable base to support the foot during ground contact. The sole must also provide traction, protection, and a durable wear surface. It must have an extremely durable bottom surface to contact the ground, together with a shock absorbing midsole to absorb the considerable force to which the foot and leg are subjected during the repeated ground contact which occurs during running. In addition, protruding traction members, or cleats, are desirable on the ground engaging portions of the bottom surface for certain sports such as baseball and soccer.
Cleats of soles are traditionally molded with natural materials, such as rubber, or synthetic materials, such as high abrasion thermoplastic polyurethanes (xe2x80x9cTPUsxe2x80x9d). TPUs commonly used in such applications have a Shore A hardness of about 80 to 100, as measured by ASTM Method D-2240-91. Representative useful TPUs are sold by the Bayer Corporation under the trademarks TEXIN(trademark) and DESMOPAN(trademark). However, such cleats tend to become clogged with debris during use, and wear down with repeated use.
As explained more fully in U.S. Pat. No. 5,832,636 to Lyden et al, the disclosure of which is hereby incorporated by reference, one method for preventing cleats from becoming clogged during use is to include an adhesion prevention material having both a low coefficient of friction and a low wettability with respect to water in a portion of the ground engaging surface. Preferred adhesion prevention materials include using xe2x80x9cneat polymers,xe2x80x9d such as solid polytetrafluoroethylene (xe2x80x9cPTFExe2x80x9d), compounded with xe2x80x9cpigments, fillers, reinforcements, lubricants, processing aids, and curativesxe2x80x9d to make useful compositions having a coefficient of friction preferably less than 0.4. In order to prevent a reduction in traction, the tips of the cleats in Lyden et al. remain substantially free of such adhesion prevention material.
U.S. Pat. Nos. 5,143,963 and 5,286,773 to Sterling, et al., the disclosures of which are hereby incorporated by reference, disclose a composition of matter formed by melt-blending a thermoplastic polymer with a concentration of fluorocarbon additive ranging between 0.01% to 1%. Disclosed fluorocarbon additives include perfluoropolyether (xe2x80x9cPFPExe2x80x9d), such as FLUOROGUARD(copyright) Polymer Additive manufactured and sold by the E.I. DuPont DeNemours Corporation. Sterling et al. discloses the tensile strength, surface energy, and water contact angles of the various compositions disclosed, and suggests that because of the high hydrophobicity and low surface energy, xe2x80x9cstickingxe2x80x9d of the composition to a mold during the molding process is reduced, thereby enhancing mold release. These references are silent regarding the durability of the compositions disclosed, and they neither teach nor suggest using such compositions in the ground engaging portions of an article of footwear for improved durability.
U.S. Pat. No. 5,864,968 to Mann, the disclosure of which is hereby incorporated by reference, discloses a shoe insole having a container containing liquid PFPE for absorbing the impact of a foot wearing the shoe. There is no teaching or suggestion in Mann to use or combine PFPE, or other disbursed fluorocarbon additives, with polymers to provide wear resistant ground engaging portions of the sole of a shoe.
Thus, despite the disclosures of the above-discussed patents, there remains a need for an article of footwear having a sole with durable ground engaging portions, particularly at the tips of any protruding traction members or cleats, without adversely affecting the traction of these ground engaging portions.
An article of footwear, such as an athletic shoe, according to the present invention includes an upper secured to a sole having a ground engaging portion with a wear resistant material composed of a thermoplastic polymer blended with 0.1% or more of a fluorocarbon additive. The upper limit of additive is the amount of additive that can be associated with the molten TPU during melt processing, typically 2.5 to 3% of the total composition, depending on the particular ingredients selected. In a preferred embodiment, the sole has ground engaging protrusions or cleats with each cleat composed of the wear resistant material, and the wear resistant material is a blend of TPU of Shore A hardness of from 80-100 as measured by ASTM Method D-2240-91, such as Bayer Corporation""s TEXIN 285(trademark) or DESMOPAN 8785(trademark), blended with more than 0.1% PFPE, such as DuPont""s FLOUROGUARD(copyright) Polymer Additives having molecular weights ranging from 1500 up to 15,000, preferably 4,700 grams/mole.
Various advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there are illustrated and described preferred embodiments of the invention.